In a Long Term Evolution (LTE) system, a mobile terminal having data or other signaling to transmit to the network may generate a buffer status report. While various types of uplink signaling may be transmitted from the mobile terminal to an access point, such as an evolved Node B (eNB), the uplink signaling may include an RLC STATUS PDU that is to be reported to an eNB for downlink transmission, a service establishment request that is to be transmitted to an eNB in the instance of a mobile originated (MO) call, radio resource control (RRC) reconfiguration complete signaling that is to be transmitted to an eNB to complete the procedure or acknowledgement/negative acknowledgement feedback for the transmission control protocol (TCP) layer.
The buffer status report is to be provided to an access point, such as an evolved Node B (eNB), so as to provide the access point with information regarding the buffer size in which the data or other signaling that the mobile terminal desires to transmit to the network is stored. The transmission of the buffer status report to the access point effectively requests an uplink grant.
The buffer status report is to be transmitted from the mobile terminal to the access point on the physical uplink shared channel (PUSCH). In an instance in which the mobile terminal does not have an uplink grant on PUSCH, the mobile terminal may initially transmit a scheduling request on the physical uplink control channel (PUCCH) to acquire the uplink grant on PUSCH that is required to report the buffer status report to the access point.
An LTE system also provides for acknowledgment/negative acknowledgment (ACK/NACK or A/N) repetition. ACK/NACK repetition is utilized to improve the PUCCH performance in an instance in which the uplink channel quality is poor for a particular mobile terminal. Once a mobile terminal is configured for ACK/NACK repetition, the mobile terminal will repeat the ACK/NACK transmission on PUCCH a predetermined number of times, such as 2, 4 or 6 times. During the time period that the mobile terminal is transmitting the repeated ACK/NACK transmission, the mobile terminal should not transmit other uplink signals. As such, in an instance in which there is a continuous downlink transmission to a mobile terminal and the mobile terminal is configured for ACK/NACK repetition, the mobile terminal may be unable to transmit the scheduling request to the access point to request an uplink grant since the mobile terminal is not allowed to transmit any other uplink signals while the mobile terminal is transmitting the repeated ACK/NACK transmissions.
A scheduling request counter may also be established to track the number of times that the mobile terminal attempts to transmit the scheduling request and to define the maximum number of times that the mobile terminal may attempt to transmit the scheduling request prior to experiencing a dedicated scheduling request (D-SR) failure and transitioning to a random access procedure. Thus, in instances in which the mobile terminal attempts to transmit the scheduling request, but is unable to do so because of the repeated ACK/NACK transmissions occurring during a continuous downlink transmission, the scheduling request counter may be increased in some situations. In instances in which the downlink transmission is sufficiently long so that the mobile terminal repeatedly fails to transmit the scheduling request and the scheduling request counter eventually satisfies a predefined threshold, the mobile terminal may experience D-SR failure. A random access procedure may then be triggered due to the D-SR failure in an effort to provide for the uplink transmission.
Once the random access procedure has been triggered, the medium access control (MAC) of the mobile terminal may select the preamble and the PRACH resource for transmission. The mobile terminal may also indicate the related information to the PHY layer, but the PHY layer may be unable to transmit the preamble and the PRACH resource due to a collision with the ACK/NACK transmissions. In this instance in which there is a continuous downlink transmission to the mobile terminal, the mobile terminal may be effectively deadlocked such that even if the mobile terminal had an opportunity for a uplink transmission at a later point in time, the mobile terminal would wait until another buffer status report and/or scheduling request is triggered and another random access procedure is initialized to resolve the deadlock since following a D-SR failure any subsequent scheduling request will also trigger a random access procedure.
The limitation upon the ability of a mobile terminal to obtain an uplink grant may happen infrequently in a frequency division duplex (FDD) scenario since the mobile terminal will have a uplink opportunity on every subframe. In FDD, the access point, such as the eNB, could reserve one or more subframes to be utilized for a scheduling request even in instances in which ACK/NACK repetition is configured. However, in a time division duplex (TDD) scenario, there are fewer uplink subframes such that the limitations upon obtaining an uplink grant may occur more frequently. For example, TDD configuration #2, which may be compatible with a time division synchronous code division multiple access (TD-SCDMA) system has only two uplink subframes within a radio frame as shown in FIG. 1 in which the uplink, downlink and special subframes are designated U, D and S, respectively.
Even if the ACK/NACK repetition factor is the lowest value, e.g., 2, once the access point, such as the eNB, schedules one downlink subframe, there would be at least one radio frame unavailable for the transmission of a scheduling request or a preamble. As such, a mobile terminal proximate the edge of a cell that is receiving a continuous downlink transmission may likely have to wait until the downlink transmission is completed in order to have an opportunity to request the uplink for the transmission of uplink data or signaling, thereby delaying the uplink transmission which may be disadvantageous in some instances.
In order to avoid D-SR failure and reliance upon a random access procedure, it has been proposed that the scheduling request counter not be increased in response to the failure to transmit a scheduling request due to repeated ACK/NACK transmissions. In this scenario, however, the mobile terminal may still be unable to notify the access point of the uplink data or other signaling that the mobile terminal desires to transmit via an uplink while the continuous downlink transmission proceeds and the repeated ACK/NACK transmissions are made during the various uplink opportunities. The mobile terminal in this instance would be required to wait until the downlink transmission was completed prior to having the opportunity to provide the buffer status report to the access point, thereby again disadvantageously delaying the request for an uplink grant.